In a normal dielectric material, upon the application of an electric field, positive and negative charges will be displaced from their original position—a concept which is characterized by the dipole moment or polarization. This polarization, or displacement, will vanish, however, when the electric field returns back to zero. On the other hand, in a ferroelectric material, there is a spontaneous polarization—a displacement which is inherent to the crystal structure of the material that does not disappear in the absence of the electric field. The direction of this polarization can be reversed or reoriented by applying an appropriate electric field.
Ferroelectric polymers are a class of ferroelectric materials potentially targeted for use in non-volatile memory applications. Integrated circuits which use ferroelectric polymers are generally referred to as ferroelectric polymer memory devices (FPMDs). These devices typically comprise intersecting bottom and top metal electrodes and an intervening ferroelectric polymer film (FPF). The FPF constitutes the core of the memory bit for the FPMD. Because transistors are not required, FPMD memory arrays can be stacked in three dimensions. This means they can be used to fabricate higher-density memories than are otherwise possible using conventional silicon-based transistor technologies.
However, conventional FPMD manufacturing methods are not without their problems. One such problem includes the ability to pattern multiple electrode layers without physically damaging or degrading the ferroelectric properties of the FPE. This can be a concern when fabricating FPMDs using damascene and subtractive metal patterning processes and/or when using conventional materials such as aluminum to form the electrodes. The etch processes used to form damascene structures can damage the FPE in regions where electrodes are formed. This is because intervening FPE regions can be exposed to etchants during damascene processing. On the other hand, subtractive etch processes, while not as damaging to the FPE in critical locations as damascene processes, are inherently non-uniform. As the number of electrode levels increases, so too does surface non-uniformity. For multi-level electrode devices, non-uniformities can become so severe that they impact the ability to pattern/etch the electrodes. Finally aluminum, while relatively easy to etch, can diffuse into the FPE and over time and position it, thereby affecting its ferroelectric properties. To the extent that FMD's ferroelectric properties are affected by any one of these, the FPMD's functionality, reliability and/or yield can be impacted.
It will be appreciated that for simplicity and clarity of illustration, elements in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Where considered appropriate, reference numerals have been repeated among the drawings to indicate corresponding or analogous elements.